Determination de l'age et de la croissance de la coryphene, Coryphaena hippurus, des cotes tunisiennes par l'analyse des microstructures des otolithes.

Determination of age and growth of dolphinfish, Coryphaena hippurus, off Tunisia by otolith microstructure analysis. The age of Coryphaena hippurus was estimated by otolithometry using daily increments of the sagitta. A total of 120 sagittae were extracted from juvenile specimens collected off the Tunisian coast during the 2005 fishing season (August to December). The fork length of the samples varied between 24 and 65 cm. The number of daily increments varied between 53 and 230 for females, 62 and 239 for males, and situated these fish between 2 and 8 months old. The regression indicated a strong relationship between the number of increments on the sagitta and the fork length (cm): y = 0.2107 x + 15.094; (r2 = 0.96), and that the growth rate was 2.11 mm/day. The Von Bertalanffy growth equation was fitted to mean back-calculated length-age data resulting in the following parameter values: for females (L[infinity] = 97.50 cm, K = 1.499 year-1, t0=0.046 year); for males (L[infinity] = 100.50 cm, K = 1.430 year-1, t0=0.042 year); and for the two mixed sexes (L[infinity] = 100.5 cm, K = 1.418 year-1, t0=0.048 year). The length-weight relationship was significantly isometric for the two sexes with values of "b" equal to 3.0281 for females, 3.0893 for males, and 3.0669 for the two mixed sexes. A higher weight growth rate, however, was observed for males over 40 cm of size. This difference became more pronounced with the individual size (age) and with bony crest frontal development in males (sexual dimorphism).